Composition of magnetic core material and method of producing same



May 1, 1962 K. SIXTUS ETAL 3,032,503

COMPOSITION OF MAGNETIC CORE MATERIAL AND METHOD OF PRODUCING SAME Filed June 4, 1959 B in Gauss lnven/vrzs KLAUS .5/X7'U5 KARL RE/CHEL United States Patent 3,032,503 COMPOSITION OF MAGNETIC CORE MATERIAL AND METHOD OF PRODUCING SAME Klaus Sixtus, Bad Homburg, and Karl Reichel, Kelkheim (Taunus), Germany, assignors to Licentia Patent-Verwaltungs-G.m.b.H., Hamburg, Germany Filed June 4, 1959, Ser. No. 818,126 Claims priority, application Germany June 4, 1958 6 Claims. (Cl. 252-625) The present invention relates to a new composition of magnetic core material and method of producing the same. More in particular, the present invention relates to a new composition of magnetic core material and a method of producing such magnetic core material having a substantially rectangular hysteresis loop.

Magnetic core material having a substantially rectangular hysteresis loop is used for example, in switches, for storage purposes, or in magnetic amplifiers.

It has already become known to provide core material having a substantially rectangular hysteresis loop comprising magnetizable ceramic material containing iron oxide, magnesium oxide, and manganese oxide.

The particular composition of these known core materials and the method of producing such magnetic core materials has proved, however, unsatisfactory, complicated and costly.

These known core materials have a hysteresis loop which is characterized by a peak induction B of from 1500 to 2000 gausses, a coercive force of from 0.7 to 2 oersteds, and a remanence-peak induction ratio B,:B,:0.85 to 0.95, and a squareness ratio R =0.8 to 0.9. R is defined by the equation Rs: B,(at H 13 being the induction obtained by maximum modulation of the loop up to field intensity H B, being the induction at a field intensity of According to another improved method of producing core material, ferrites on an iron oxide and cobalt oxide basis are subjected to the influence of heat and a magnetic field. However, this method and the core material so obtained still are unsatisfactory. According to this known method a hysteresis loop is obtained having a remanence B of up to 3000 gausses, a coercive force of from 5 to 80 oersteds, and a squareness ratio R, from 0.5 to 0.95. Even these values are obtained only in the direction in which the core material has been exposed to the magnetic field during heat treatment, whereas the hysteresis loop has retained its normal, S-shaped configuration in all other directions.

All these known core materials and the methods of producing them are unsatisfactory. In addition to a rectangular hysteresis loop it is extremely desirable for several purposes to have a high remanence but at the same time a low coercive force. Such core materials are used, for example, in magnetic amplifiers, in switching and counting devices and in digital computers. The known core materials, their particular composition and the methods for producing them do not meet these requirements. They do not accomplish the triple purpose of providing for core materials having, at the same time, a substantially rectangular hysteresis loop, a high remanence and a low coercive force. Moreover, the last mentioned method of exposing the core material to the influence of heat and a magnetic field is complicated and costly.

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With the foregoing in mind, it is an object of the present invention to provide for a new composition of magnetic core material, which has a substantially rectangular hysteresis loop and, at the same time, both a high remanence and a low coercive force.

It is another object of the invention to provide for a simple and effective method of producing magnetic core material having a substantially rectangular hysteresis loop, a high remanence, and a low coercive force.

These objects are achieved by the present invention, which has found a new composition of core material to be highly superior to any of the known compositions. According to the invention, the core material is composed of the following materials in the following ratio:

0.8 to 1 mol Fe O :0.4 to 0.7 mol ZnO:0.00l to 0.05 mol C00, plus a predetermined amount of NiO so that the mo] total of ZnO, C00, and NiO is one.

According to another, preferred embodiment of the percent of the total; in this case the mol total of ZnO,

C00, NiO and CuO is one. The mol ratio between the iron oxide and the total of the other oxides is in the range of from 0.8 to 1:1.

The presence of copper oxide (CuO) greatly facilitates the sintering process, referred to further below, without substantially impairing the excellent magnetic characteristics of the core material.

It has been discovered that ferrites with a smaller percentage of iron oxide ((Fe O than the stoichiometric composition will produce a substantially rectangular hysteresis loop, without requiring a treatment in a magnetic field and exposure to heat. This is particularly true where the abovementioned composition of the invention is chosen. The new method for producing a magnetic core material with a substantially rectangular hysteresis loop, a high remanence and a low coercive force can therefore dispense with this step of exposing the material to heat in a magnetic field. According to the method of the present invention, the metal oxides or compounds giving off the oxides when heated, are pulverized, mixed and subjected to a first sintering process in air and at a temperature of from 800 to 1000 C., whereupon the cores are molded, which are then subjected to a second, main sintering operation in oxygen and at a temperature of from 1200 to 1400" C.

According to another embodiment of the method of the invention, the cobalt compound, which is to furnish the necessary share of C00 in the core material is added only after the other substances have gone through the aforementioned first sintering operation.

More in detail, a certain quantity of iron oxide is mixed, for example with nickel carbonate, zinc carbonate and cobalt carbonate of such quantities, that the abovedescribed mol ratio is obtained. The mixture is then finely ground, with water being added, in a grinding mil-l as, e.g., a ball mill; Two hours will be sufficient to effect this wet grinding operation. This finely ground mixture is then dried. Thereafter, it is exposed to a first sintering process. The sintering is done in air or oxygen at a temperature taken from the range of from 800 to 1000" C., and for a period of about two hours. The sintered product is ground again in a suitable grinding mill, such as a ball mill, with water being added. The product is dried and then used as the material for molding annular cores, in a manner known per se. These cores are then subjected to a second, main sintering operation, which is done in oxygen and at a temperature of from 1200 to 1400 C.

The invention will be'even better appreciated upon reading the following examples in conjunction with the accompanying drawing, which is a diagram showing the advantageous characteristics of the core material of the composition and produced according to the method of the present invention.

' Example I 58.3 grams iron oxide (Fe O 17.85 grams nickel carbonate, 24.4 grams zinc carbonate and 2.1 grams cobalt carbonate are taken, which amounts correspond to the mol ratio of 0.98 mol Fe O :0.'37 mol NiO:0.58 mol ZnO:0.05 mol CoO. These substances are mixed in a ball mill'for about two hours during which process Water is added. The mixture is then removed from the ball mill and dried. Thereafter, the dried mixture is sintered for a first time for two hours at 950 C. in air. The sintered product is then wet ground in a ball mill and thereafter dried again. Thereupon the dried product is subjected to a pressure of 0.5 ton/cm. in a mold and shaped into an annular core. The core is then subjected to a second, final, sintering process for about two hours at a temperature of 1250 0, this time not exposed to air but to oxygen. Thereafter it is cooled in the sintering oven proper.

The characteristics of the hysteresis loop of the annular core obtained by this treatment are shown in the accompanying drawing and are as follows: B =3l00 gausses; coercive force H =0.75 oersted; ratio B /B 0.97; squareness ratio R =0.94. The specific electric resistance is 9 centimeters.

Example vll 553 grams iron oxide (F6 03), 183.2 grams nickel carbonate and 243.8 grams zinc carbonate are mixed with water for about two hours, whereupon the mixture is dried. The dried mixture is then exposed to-a first sintering process in oxygen at a temperature of 900 C. and for a period of two hours. To 100 grams of this mixture there are added 2.1 grams cobalt carbonate and 1.7 grams iron oxide (Fe O so as to obtain a composition having a ratio of 0.96 mol Fe O :0.38 mol NiO:0.58 mol ZnO:0.04 mol C00. The mixture is then wet ground and dried. The ground and dried product is then pressed as in Example I to the shape of an annular core. The annular cores are then sintered in oxygen at a temperature of 1250" C. for two hours.

A magnetic core material is obtained having a substantially rectangular hysteresis loop with the following characteristics: B =2540 gausses; H =0.85 oersted, ratio B /B =0.96; R =0.93. The specific electric resistance is 2.10 9 centimeters.

Example III 553 grams iron oxide (Fe O 183.2 grams nickel carbonate and 24.3.8 grams Zinc carbonate are mixed, dried and sintered in oxygen for two hours at a temperature of 900 C. To 100 grams of this sintered mixture there are added 0.64 gram cobalt carbonate and 2.2 grams iron oxide so as to have a composition with the ratio of 0.98 mol Fe O :0.398 mol NiO:0.59 mol ZnO:0.012 mol CoO. This mixture is then wet ground and dried whereupon the annular cores are formed. These are then exposed to a sintering process in oxygen at a temperature of 1250 C. and for a period of two hours.

The hysteresis loop of the magnetic core has the following characteristics: B =2900 gausses; H =0.5 oersted; ratio B,/B =0.95; R =0.83.

The foregoing examples, in conjunction with the accompanying diagram show, that magnetic cores areobtained having an excellently rectangular hysteresis loop with high remanence and, at the same time, a low coercive force. This is obtained even though the cores were not subjected to heat in a magnetic field.

'Itwill be understood thatthis invention is susceptible to further modification and, accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

What we claim is: 1. As a composition of matter, magnetic coremateiial having a substantially rectangular hysteresis loop, composed of iron oxide, zinc oxide, cobalt oxide, and nickel 3. ,A method for producing magnetic'core material having a substantially rectangular hysteresis loop and being composed of iron oxide, zinc oxide, cobalt oxide, and nickel oxide in a ratio of from 0.8 to 1 mol Fe o zfrom 0.4 to 0.7 mol ZnO:from 0.001 to 0.05 mol C00 and a determined amount of nickel oxide so that the mol total of the shares of ZnO, C00, and NiO is one, comprising the steps of pulverizing and mixing- Fe O ZnO, C00 and NiO, subjecting the same to a first sintering'process in air ata temperature of from 800 to 1000 C., molding the magnetic cores, and sub: jecting the latter to a second, main sintering process in oxygen at a temperature of from 1200 to 1400 C.

4. .A method for producing magnetic core material having a substantially rectangular hysteresis loop and being composed of iron oxide, zinc oxide, cobalt oxide, and nickel oxide in a ratio of from 0.8 to 1 mol Fe o zfrom 0.4 to 0.7 mol ZnOzfrom 0.001 to 0.05 mol C00 and a determined amount of nickel oxide so that the mol total of the shares of ZnO, C00 and NiO is one, comprising the steps of pulverizing and mixing Fe O ZnO and NiO, subjecting the same to a first sintering process in air at a temperature of from 800 to 1000 (1., adding a predetermined amount of cobalt carbonate to the sintered product, molding the magnetic cores, and subjecting the latter to a second, main sintering process in oxygen at a temperature of from 1200 to 1400" C.

5. A method for producing magnetic core material having a substantially rectangular hysteresis loop and being composedof iron oxide, zinc oxide, cobalt oxide, and nickel oxide in a ratio of from 0.8 to 1 mol Fe O zfrom 0.4 to 0.7 mol ZnOzfrom 0.001 to 0.05 mol C00 and a determined amount of nickel oxide so that the mol total of the shares of ZnO, C00 and NiO is one, comprising the steps of pulverizing and mixing iron oxide (Fe Q nickel carbonate, zinc carbonate and cobalt carbonate, subjecting the same to a first sintering process in air at a temperature of from 800 to 1000 C., molding the magnetic cores, and subjecting the latter to a second main sintering process in oxygen at a temperature of from 1200 to 1400 C.

6. A method for producing magnetic core material having a substantially rectangular hysteresis loop and being composed of iron oxide, zinc oxide, cobalt oxide, and nickel oxide in a ratio of from 0.8 to 1 mol Fe O :from 0.4 to 0.7 mol ZnOzfrom 0.001 to 0.05 mol C00 and a determinedamount of nickel oxide so that the mol total of the shares of ZnO, C00 and NiO is one, comprising the steps of pulverizing and mixing iron oxide (Fe O nickel carbonate and zinc carbonate, subjecting the same to a first sintering process in air at a temperature of from 800 to 1000 C., adding a predetermined amount of cobalt carbonate to the sintered product, molding the magnetic cores, and subjecting the latter to a second,

1200 to 1400;" c.

main sintering process in oxygen at a temperature of from (References on following page).

6 References Cited in the file of this patent FOREIGN PATENTS 752,659 Great Britain July 11, 1956 UNITED STATES PATENTS 1,100,865 France Apr. 13, 1955 2,656,319 Berge Oct. 20, 1953 1,160,057 France Feb. 24, 1958 2,723,239 Harvey Nov. 8, 1955 5 OTHER REFERENCES 2,736,708 Crowley et a1. Feb. 28, 1956 RCA Review, Harvey et a1., September 1950, pp. 344- 2,860,105 Gorter et a1. Nov. 11, 1958 3 

6. A METHOD FOR PRODUCING MAGNECTIC CORE MATERIAL HAVING A SUBSTANTIALLY RECTANGULAR HYSTERESIS LOOP AND BEING COMPOSED OF IRON OXIDE, ZINC OXIDE, COBALT OXIDE, AND NICKEL OXIDE OXIDE IN A RATIO OF FROM 0.8 TO 1 MOL FEO3: FROM 0.4 TO 0.7 MOL ZNO: FROM 0.001 TO 0.05 MOL COO AND A DETERMINED AMOUNT OF NICKEL OXIDE SO THAT THE MOL TOTAL OF THE SHARES OF ZNO, COO AND NIO IS ONE, COMPRISING THE STEPS OF PULVERIZING AND MIXING IRON OXIDE (FE2O3), NICKEL CARBONATE AND ZINC CARBONATE, SUBJECTING THE SAME TO THE FIRST SINTERING PROCESS IN AIR AT A TEMPERATURE OF FROM 800 TO 1000* C., ADDING A PREDETERMINED AMOUNT OF CABALT CARBONATE TO THE SINTERED PRODUCT, MOLDING THE MAGNETIC CORES, AND SUBJECTING THE LATTER TO A SECOND, MAIN SINTERING PROCESS IN OXYGEN AT A TEMPERATURE OF FROM 1200 TO 1400* C. 